The present invention relates to an optical coupler having a semiconductor optical device and to electronic equipment using the same, and more particularly, relates to an optical coupler for use in optical communication links and so forth for sending and receiving optical signals with an optical fiber as a transmission medium, and electronic equipment using the same.
Conventionally, there have been known optical couplers coupling semiconductor optical devices such as LEDs (Light Emitting Diodes) and PDs (Photo Diodes) to optical fibers, which have been used for optical communications between equipments, at home and in automobiles.
As these optical couplers, those manufactured utilizing transfer molding of transparent resin as shown in FIG. 10 are widely used. An optical coupler 101 shown in FIG. 10 is structured such that an semiconductor optical device 103 disposed on a lead frame 104 is encapsulated with a transparent resin 110, and the semiconductor optical device 103 is optically coupled to an optical fiber 102 through a lens 108 formed out of part of the transparent resin 110. The semiconductor optical device 103 is electrically connected to the lead frame 104 via wire 105. Further, in some cases, a semiconductor device for driving and controlling the semiconductor optical device 103 is mounted on the lead frame 104. Such optical couplers utilizing transfer molding have a characteristic of being easily manufactured at low costs compared to, for example, optical couplers using a glass lens.
It is known that doping resin molding materials with fillers allows adjustment of a coefficient of linear expansion and heat conductivity, and so semiconductor devices which do not need an optical property are encapsulated with molding resins (normally black) added with fillers. Since the above-mentioned optical coupler 101 using the transparent resin 110 put emphasis on the optical property, it was difficult to add the resin with a filler (or the resin is added only with a small amount of the filler), and so the optical coupler 101 had a problem in environmental resistance (including thermal shock resistance and heat dissipation).
Accordingly, as shown in FIG. 11, there has been proposed an optical coupler with a modified structure in which encapsulating is made by a color molding resin added with a filler (see, e.g., JP 2000-173947 A). In an optical coupler 201 shown in FIG. 11, the semiconductor optical device 203 is mounted on a lead frame 204 with only an optical portion 206 thereof being adhered to a glass lens 208, and electrodes around the optical portion 206 of the semiconductor optical device 203 are electrically connected to the lead frame 204 via wire 205. Then, transfer molding is conducted with a color molding resin 209 added with a filler, which makes it possible to encapsulate the semiconductor optical device 203 and the wire 205 with the color molding resin 209 without the color molding resin 209 blocking an optical path through which light comes into and goes out from the semiconductor optical device 203.
As shown in FIG. 11, the optical coupler is structured such that the glass lens 208 is mounted on the optical portion 206 and the semiconductor optical device 203 is encapsulated with the color molding resin 209 with a part of the glass lens 208 included in the color molding resin 209. However, a practical means to perform resin encapsulating with this structure is not disclosed in JP 2000-173947 A. Generally, resin for use in transfer molding has small particles, which induces a phenomenon of resin leaking from a space of several μm. Therefore, it is considered to be difficult to realize such a structure stated in JP 2000-173947 A. Moreover, in the case of using a semiconductor optical device with a relatively large size (several mm to several dozen mm square) such as CCDs (Charge Coupled Devices), it is possible to dispose a glass lens on an optical portion. However, a semiconductor optical device with a small size (several hundred μm square) such as LEDs, which has an extremely small optical portion, needs to use a glass lens that is also extremely small in size, thereby causing problems including: (i) it is difficult to design a lens which can offer optical effects; (ii) it is difficult to manufacture a minute glass lens; and (iii) it is difficult to bond and align the optical portion and the glass lens. Further, if a glass lens that is larger than the optical portion of the semiconductor optical device is used, electrodes close to the optical portion of the semiconductor optical device are also bonded to the glass lens, which makes it impossible to conduct wire bonding.
For the above-stated optical coupler, there has also been disclosed a method with use of a resin lens. However, in the case of using the semiconductor optical device having a small size such as LEDs, its optical portion is small and so there is difficulty in practical application due to the same reasons. Further, in the case of using the resin lens, due to the heat resistance of the lens, it is necessary to perform molding with a color molding resin before the resin lens is mounted, which makes it necessary to hold the optical portion of the semiconductor optical device and a mold by pressure contact or with a minute gap so as to prevent a color resin from coming into the optical portion of the semiconductor optical device. This necessitates damage prevention of the semiconductor optical device and high-accuracy mold management (as well as deformation prevention of a lead frame), bringing about difficulty in manufacturing. Particularly in the case of the semiconductor optical device with a small size such as LEDs, it is extremely difficult to manage so as to prevent the color molding resin from coming into the optical portion while protecting wires.
Moreover, the transparent molding resin, the semiconductor optical device, the lead frame and the bonding wire are generally different in a coefficient of linear expansion. Consequently, in the range of high operating-temperatures, breaking of the bonding wire, package cracks and so forth occur, making it exceedingly difficult to manufacture the optical coupler with high reliability.